1. Field of the Invention
This invention relates to a method and a composition for controlling volume change in fast setting, fluid impermeable cementitious systems. In particular, this invention relates to a method and a composition for inhibiting wet expansion, in the hardened state, of cementitious systems containing aluminous cement, gypsum, and Portland cement by adding thereto salts of lithium.
The term "cementitious systems," as used herein, is intended to mean compositions which generally possess the characteristic of hardening under water. Such systems include cementitious waterproofings, toppings, protective coatings, and the like as well as mixtures with aggregates and water such as concrete, mortar, grout and products made therefrom.
The term "aluminous cement," as used herein, is intended to include those cementitious materials normally understood in the art to contain, as the main cementitious constituent, monocalcium aluminate (CaO.Al.sub.2 O.sub.3), such as high alumina cement and calcium aluminate cement. Examples of commercially available aluminous cements suitable for use in the invention are Lumnite by Lehigh Portland Cement Company and the high alumina cement Fondu or Secar by LoneStar LaFarge Aluminous Cement Company, Ltd.
The term "gypsum," as used herein, is intended to include gypsum such as normally understood in the art, including calcium sulfate (CaSO.sub.4) and its various forms, calcium sulfate anhydrate, calcium sulfate hemihydrate, calcium sulfate dihydrate as well as calcined gypsum, pressure calcined gypsum and plaster of Paris. Examples of commercially available gypsums suitable for use in the invention are the pressure calcined gypsums sold under the tradename "K-5" by Georgia Pacific Corporation or the tradename "Hydrostone" by United States Gypsum Company.
The term "Portland cement," as used herein, is intended to include those cements normally understood in the art to be "Portland cements" such as described in the designation ASTM C 150, with the Type I and Type III being especially preferred for use in the invention although other forms of Portland cement are suitable. The Portland cement acts to reduce the drying shrinkage and will increase the wet expansion of the composition in the present invention. Thus, other cements acting as "drying shrinkage inhibitors," although not specifically referred to as Portland cement, are also suitable for use herein and the term should be understood as encompassing such other cements. Such other drying shrinkage inhibitors may include, for example, expansion promoters, such as expansive cements, which are compatible with the other constituents of the system.
The term "wet expansion," as used herein, is intended to mean expansion of a cementitious system in the hardened state, that is, after final set, in moist conditions as determined generally in accordance with the standard test method ASTM C 157-75 for "Length Change of Hardened Cement, Mortar and Concrete."
The terms "wet expansion inhibition" and "wet expansion counteraction" are used essentially interchangably herein to describe, as a minimum, a reduction in the wet expansion of the cementitous system in the hardened state and/or advantageously maintaining a volume equal to or greater than the system placement volume, and encompass similar terms such as "wet expansion elimination."
2. Description of the Prior Art
There have been various prior attempts at providing cementitious systems meeting the needs of the construction industry, particularly in the protection, waterproofing and repair of concrete structures. Such systems are desirably non-flammable, non-toxic and set within a relatively short period of time into a hard mass or coating with sufficient strength, abrasion resistance and corrosion resistance. They should also possess impermeability to fluids, particularly liquids. At the same time, such systems should not undergo excessive hardened volume changes under either wet or dry conditions. For commercial use, these types of cementitious systems must also possess good bonding characteristics to damp or dry surfaces, early as well as long term strength and practical field workability. They should be capable of withstanding freezing and thawing as well as the action of salts, solvents and other corrosive substances.
Although there are cementitious system compositions possessing one or more of the above desirable properties, prior attempts directed to achieving all of the foregoing in one composition have had only limited success. Many compositions of blended cement exhibit wet expansion. Other compositions which include the addition of certain accelerators to reduce setting time exhibit excessive drying shrinkage. Thus, prior attempts at providing cementitious compositions of commercial value in the construction industry have generally been specific or emphasized particular properties in disregard of, or, in some instances, in detriment to other desired attributes.
U.S. Pat. No. 3,861,929 discusses the inherent shrinkage characteristics of concretes made with conventional cements which result in cracks on hardening and drying. That patent discloses an expansive cement that, during and after setting and hardening, increases significantly in volume. The expansive cement disclosed comprises a mixture consisting essentially of Portland and calcium aluminate cements and a quantity of calcium sulfate which may be in the form of gypsum. U.S. Pat. No. 3,775,143 discloses a "stressing" cement which includes Portland cement and an expanding component consisting of calcium sulfate, calcium oxide and an aluminate containing material such as aluminous cement or high alkaline calcium hydroaluminate. The cement is said to exhibit water-proofness as well as benzine-and gasproofness.
U.S. Pat. No. 3,147,129 discusses some of the problems in the basic processes for producing sulfoaluminate cements including difficulty in control of properties. The patent then discloses a sulfoaluminate cement composition said to have uniform properties and which can be used as an expansive cement upon the inclusion of suitable additives such as zinc sulfate and sodium bisulfate. The patent states that certain constituents may be added as retarders which do not cause appreciable expansion and even tend to neutralize the expansive action of the additives such as zinc sulfate and sodium bisulfate. Such constituents may comprise sucrose, hydrated lime and silica mixtures.
Compositions containing high alumina cement and Portland cement for use as a quick setting mix have been known. For example, U.S. Pat. No. 4,012,264 states that it is known that very rapidly setting and hardening cement can be produced by mixing Portland cement and high alumina cement and/or by the use of various accelerators, and discloses a calcium-aluminate and Portland cement composition including retarders and/or accelerators. High alumina cement has also been added to plaster of Paris or anhydrite plasters in order to give stronger molds or castings. T. D. Robson, High Alumina Cements and Concretes, John Wiley & Sons, N.Y., 1962, pp. 126-7, discloses that lithium salts have been suggested as accelerators for high alumina cement. However, it has been found that compositions containing alumina cement, gypsum and lithium salts as an accelerator, alone, exhibit excessive hardened drying shrinkage. In addition, compositions containing aluminous cement and gypsum alone exhibit excessive hardened wet expansion.
U.S. Pat. No. 2,339,163 discloses a composition for a protective cement coating comprising calcium aluminate cement and an inorganic additive selected from the group consisting of calcium chloride, calcium sulfate, magnesium sulfate, ferric sulfate, aluminum sulfate and carbonates of alkali metals to accelerate the setting, as well as casein to limit the rate of evaporation of water so as to prevent too rapid drying and shrinkage. It is said that the material will produce a coating which will not crack after it has set and become hardened, apparently referring to the reduction of drying shrinkage.
U.S. Pat. Nos. 4,045,237 and 4,157,263 disclose a cementitous composition possessing a high degree of impermeability to liquid and vapor and reduced long term shrinkage, composed of a particulate mixture of Portland cement, a calcined gypsum and high alumina cement. Alternatively, the composition can be composed of a particulate mixture of a high alumina cement and pressure calined gypsum.